Added member data to classes to support download resumption.

content/browser/download/base_file.h

Index: content/browser/download/base_file.h
diff --git a/content/browser/download/base_file.h b/content/browser/download/base_file.h
index 2a0994358055c89d9f84c59b1fca13c4f5076f5e..493099630bbd7e32aa130e46132ccde32a6cea47 100644
--- a/content/browser/download/base_file.h
+++ b/content/browser/download/base_file.h
@@ -33,6 +33,7 @@ class CONTENT_EXPORT BaseFile {
            const GURL& source_url,
            const GURL& referrer_url,
            int64 received_bytes,
+           const std::string& hash_state,
            const linked_ptr<net::FileStream>& file_stream);
   virtual ~BaseFile();
 
@@ -65,10 +66,16 @@ class CONTENT_EXPORT BaseFile {
   bool in_progress() const { return file_stream_ != NULL; }
   int64 bytes_so_far() const { return bytes_so_far_; }
 
-  // Set |hash| with sha256 digest for the file.
+  // Fills |hash| with the sha256 digest for the file.
   // Returns true if digest is successfully calculated.
   virtual bool GetSha256Hash(std::string* hash);
 
+  // Returns the current (intermediate) state of the hash as a byte string.
+  virtual std::string GetSha256HashState();
+
+  // Resets the current state of the hash to the contents of |hash_state_bytes|.
+  virtual bool SetSha256HashState(const std::string& hash_state_bytes);

[Randy Smith (Not in Mondays), 2011/11/22 17:37:49]

Given that this is also in the constructor, is this setter necessary?

[ahendrickson, 2011/11/22 23:46:44]

It doesn't actually get set in the constructor, but in Initialize().  The latter
calls this setter.  Otherwise, we don't really need it.

[Randy Smith (Not in Mondays), 2011/11/23 19:25:13]

Then shouldn't it be private?  I'm good with either private or eliminated (and
code incorporated into Initialize()).

[ahendrickson, 2011/12/20 00:04:14]

Made it private.

+
   // Returns true if the given hash is considered empty.  An empty hash is
   // a string of size kSha256HashLen that contains only zeros (initial value
   // for the hash).
@@ -114,6 +121,9 @@ class CONTENT_EXPORT BaseFile {
   // is set.
   scoped_ptr<crypto::SecureHash> secure_hash_;
 
+  // The hash state is stored here on creation.
+  std::string initial_hash_state_;

[Randy Smith (Not in Mondays), 2011/11/22 17:37:49]

Why can't you just unpickle in the constructor directly into secure_hash_?

[ahendrickson, 2011/11/22 23:46:44]

Initialize() would reset it.

[Randy Smith (Not in Mondays), 2011/11/23 19:25:13]

That seems like an incomplete answer, since we control the code in Initialize()
too :-} (i.e. it begs for the question "Why couldn't we avoid resetting it in
Initialize()?").  Looking at the code, I think the answer I was looking for was:
We don't know whether we want to unpack the hash until we get to Initialize()
(because Initialize() gets the "calculate_hash_" argument).  

That brings up the question of whether the hash unpack should be in the
constructor or in Initialize().  The rule of thumb I have for constructor vs.
Initialize is that if something can return an error it should be in Initialize,
otherwise it should/could be in the constructor, and setting the hash doesn't
involve any possible error returns.  Looking at all the constructions I could
easily find (DFM for DF creation, SFM for SF creation), they're all immediately
followed by initialization.  So we *could* move the hash calculation into the
constructor if we want to.

Given that, I'm inclined to say that we should.  I really don't like tossing
extra data elements into classes; it expands complexity and testing in a subtle
way.  And there's no real need for this one--it's lifetime is just
construction->Initialize.  Alternatively, we could shift the hash argument to
initialize; that would be a simpler code change, and would allow us to get rid
of this member variable (which is my primary goal).  Abstractly, I'm inclined to
think this belongs in the constructor, though.

[ahendrickson, 2011/12/20 00:04:14]

Moved the hash initialization into the constructor.

+
   unsigned char sha256_hash_[kSha256HashLen];
 
   // Indicates that this class no longer owns the associated file, and so